I think there are numerous subjects within this novel that could be studied further that would make an interesting research paper.
I think certainly (to go a somewhat easy route) you could pick any of the Japanese traditions, religions or cultural elements presented in the novel and study them further.
If you wanted to choose a more difficult (but certainly intersting and possibly more impressive to a college professor) you could consider this: one of my Chinese exchange students discussed the book and the film with me at length this year. She said that the portrayal of Japan and the "Geisha culture" in the book very obviously lacked authenticity. Of course, as an American who has not read a lot of Japanese literature, I was unaware of this missing element. She said that to anyone living in Asia, the book sounds obviously written by an American who basically did a lot of historical study to write it. Possibly you could look into this and see what has been written about the fact that an American wrote a very personal (although fictional) account of a Japanese woman's experience. Because of this, what exactly what missing? I think this could also be tied in to the film. This student again said that what the book lacked (to her and other Asians) was even more lacking in the film. She said there is a very obvious cultural element to Chinese and Japanese film. As she put it (laughing), "It is a story about Japan, staring Chinese actors, and directed by an American. How could that possibly come out right?!"
I certainly think as a college senior you should challenge yourself as you consider what to write about - but also, seek a topic that has plenty of published material to make the research part a little easier.